UP-REGULATION OF OXYTOCIN RECEPTORS IN PORCINE ENDOMETRIUM BY ADENOSINE-3',5'-MONOPHOSPHATE

Porcine endometrial cells (a mixture of epithelial, stromal, and gland ular cells) were examined for the presence of oxytocin (OT) receptors using a cell culture system and a I-125-labeled OT antagonist. Binding specificity was tested in displacement studies with various related p eptides. Scatchard analyses revealed the presence of a binding site wi th a dissociation constant (K-d) = 0.9 nM and a capacity of 1.9 fmol/1 0(5) cells. These cells, which were obtained from prepubertal gilts an d thus had not been exposed to endogenous ovarian steroids, were used as a model to evaluate the possible action of ovarian steroids and int racellular cAMP on OT receptors. Although ovarian steroids showed no e ffect on OT receptors, forskolin (an adenylate cyclase activator) and dibutyryl cAMP caused 1.5- to 1.6-fold increases in specific binding o f OT without changing the binding affinity. When the endometrial cells were exposed to OT (0.1-1000 nM) in combination with arachidonic acid (10 mu M), OT stimulated prostaglandin F-2 alpha secretion in a dose- dependent manner. These results indicate the presence of functional OT receptors in prepubertal porcine endometrial cells and suggest that t he concentration of OT receptors may be regulated by one or more subst ances that raise intracellular cAMP levels.